What Zenvon said =)
It really depends on your gear and what content you're raiding currently. While there are some very rough guidelines (haste > all below a certain ilvl, haste >= mastery for single target after a certain point), the rest is up to your simming and optimizing for yourself.

If you want the simple answer that will minimally reduce your single target damage but help your raid a lot and boost your overall DPS, go Mastery >= Haste for the entirety of SoO, this goes for both Ele and Enh. Lots of AoE components, and the single target fights don't warrant the tiny tiny boost to your focused DPS u would get out of changing your prio.

Haste > mastery by a very small percentage on pure single target fights. Mastery > haste the moment you start to cast CL at all. This is because CL has a 1.5s base cast time and you'll be close to the 1.1s cast times with even 8-10k haste rating. Mastery will drastically up your aoe damage because of the CL procs it can give. Most ele shamans are going pure mastery (after reaching a decent amount of haste, 9-11k~) because almost all encounters in siege benefit from you being an AOE beast and the small dps loss on fights like Juggs doesn't really mater in the long run.

Armory: us.battle.net/wow/en/character/skywall/S%C3%A5rah/advanced
well im only doing flex up to 15 ppl but normally im doing around 100k single target im not sure if that is good or bad

Quick Sim says 135 max in your gear atm, so if you're barely pushing 100k ur doing pretty badly tbh.
Try using the addon "Elementarist" to help you with your rotation while you learn, it's simple and straightforward and requires little to no tuning or editing.
Also make sure you are always, always casting ofc, something players new to caster DPS often aren't used to.

I'm having trouble as well. I'm only pulling 55k dps max since switching to elemental, and even using Elementarist lol I honestly don't know what I'm doing wrong. It's probably gear related so I don't know. Here's a link to my armory if anyone is curious. http://us.battle.net/wow/en/characte...ardamus/simple

Haste > mastery by a very small percentage on pure single target fights. Mastery > haste the moment you start to cast CL at all. This is because CL has a 1.5s base cast time and you'll be close to the 1.1s cast times with even 8-10k haste rating. Mastery will drastically up your aoe damage because of the CL procs it can give. Most ele shamans are going pure mastery (after reaching a decent amount of haste, 9-11k~) because almost all encounters in siege benefit from you being an AOE beast and the small dps loss on fights like Juggs doesn't really mater in the long run.

1) Haste is not always better than mastery for single target fights. It is entirely dependent on gearing and talent choices. There are no absolutes with gearing, as it is based on the values of intellect, crit, mastery, and haste, not just one or the other. There are numerous times when simcraft has told me to push more mastery than haste for single target.

I'm having trouble as well. I'm only pulling 55k dps max since switching to elemental, and even using Elementarist lol I honestly don't know what I'm doing wrong. It's probably gear related so I don't know. Here's a link to my armory if anyone is curious. http://us.battle.net/wow/en/characte...ardamus/simple

In that gear it's small wonder. You have absolute crap trinkets etc...
Also, Haste > all at your gear lvl. Try reaching 9-10k Haste before going Mastery on reforges and gems.

The best advice is to just look at SimC and do lots of reforge plots and scaling checks. If your reforge plot tells you to drop haste for mastery, it's most likely a net gain, even on single target. Haste, because of it's very nature, will be more or less valuable depending on certain values, and there will always be stat bumps and valleys to be aware of.

Along with that, if you spend the majority of the fight GCD-capped (because of the Meta or EB, ignoring Lust/Hero), you're doing it wrong, and some of your haste is going to waste.

At the gear level I'm at, if I run UF, Mastery is worth more than Haste. If I'm running EB, they're about equal, with Mastery slightly on top for now.

The base cast time for chain lightning is 2 seconds. Among other things, shamanism reduces the cast time of chain lightning by 0.5sec. Put those two together and chain lightning is a 1.5sec cast for elemental, so he was right.